In a medium size camera popularly used recently, film advancing, rewinding, and the shutter cocking can be accomplished by a built-in motor. Sometimes an automatic focus control function and/or an automatic exposure control function are added. Such fully automatic functions are applied even to large size camera.
A known film advancing and rewinding device of cameras will now be examined in detail. The known device consists of more than a hundred parts in which an electromotive film advancing element for advancing film frame by frame when taking a picture and an electromotive film rewinding element for rewinding film back into a film magazine after using a roll of film completely includes a unidirectional motor and a group of reduction gears. The rotational force transferring means transmitting the rotational force from the motor to the electromotive film advancing element or to the electromotive film rewinding element is provided between the group of reduction gears and the film advancing and rewinding element.
In the known device, the sequence of the driving force transmission and the operation of related elements linked to it during the film advancing are as follows. The driving force is transmitted from the driving motor via the group of reduction gears and the driving force transferring element to a spool to wind the film around the periphery of the spool frame by frame each time the shutter is actuated. As the film is wound, a fed frame counter is rotated by a designated angle by a sprocket engaged with and moved by perforations in the upper and lower sides of the film. At the same time, the shutter is cocked for taking a picture.
In the film rewinding, the driving force is transmitted from the driving motor via the group of reduction gears, the driving force transferring element, and a group of rewinding gears to a rewinding fork. As the bobbin of the film magazine is rotated by the rewinding fork, the film is rewound to the original state the sprocket is rotated in the opposite direction from advancing operation, and the frame counter returns to its original state.
The known film advancing and rewinding device as described above comprises too many parts and complicated organized gears which transfer the rotating force from the driving motor to the film advancing element or the film rewinding element. Therefore, the assembly of the device requires a very long time and the production cost thereof is high. Furthermore, the malfunction rate of the device is high because of the large number of parts.